The present invention relates to fluid filter devices for general, industrial applications such as sewage purification, water recovery systems in textile, plastics, etc. plants, electric power stations, swimming pool installations, compressed air systems, hydraulic or fuel systems, and the like. Without derogation from generality of the above, the invention is particularly useful in--and therefore be described with specific reference to--water irrigation systems.
Filtered water irrigation systems comprise multiple units of the following design. There is provided an elongated cylindrical housing with suitable connections to the network water supply on the one side, and to the irrigation line at the other side. Filter elements of various kinds and descriptions are installed within the housing. Usually a battery of such housings, say of 6-12 units, are connected in parallel to feed a single irrigation line, with a common, sometimes most sophisticated control system governing the operation of the various filters. Since the filter elements tend to become clogged during prolonged use thereof, the abovementioned control system includes facilities for periodically interrupting the operation of any one of the filters of the battery and cause it to undergo a flushing or rinsing stage wherein the waterflow is reversed and the filtering media included in the elements--be it a pack of discs in compact engagement, various types of perforated sheet metal or any other types known per-se in the art--become cleaned by the reversed flow of water which releases solid particles and other clogging stuff that became trapped in the filtering media.
This necessity to carry out flushing cycles from time to time (depending on the quality of the filtered water), must be automatically supervised by computer or otherwise controlled systems, which are most expensive and of a relatively poor reliability.
Among the widely used filter-media kinds there are known fluid filters of the type comprising a pack of discs or rings provided with roughened surfaces which are mounted on a common axis with the surfaces in compact engagement with each other wherein the fluid is forced to flow radially through the pack and thereby become filtered, i.e. leaving the solid particles and/or algal-type matter trapped between the discs.
Hence, a further aspect of the invention specifically concerns the method and means by which compressing or compacting of said pack is effected, and, according to a still further developed aspect thereof, also the release or loosening of the discs for periodic flushing thereof. It should be noted, in this context that while in our U.S. Pat. No. 4,665,910, issued Apr. 7, 1987, there has been disclosed means for pressing and releasing the disc pack automatically by hydraulic means--as also proposed according to the instant invention--the disclosure has been primarily assigned to a particular design suitable for reverse flushing, rinsing and disc-spinning mode of operation, as therein described and claimed.
The present invention aims, however, at providing discs tightening and releasing means readily applicable to disc-type filters of general, well-known designs. Furthermore, as will be made more clear hereinbelow, the present invention provides means readily applicable to reverse filtering flow direction as well, namely from the inner circumference of the discs radially in the outwards direction, as distinct from the usual, inwards radial flow. Conventional tightening means for filters disc packs includes, as a rule, manually-operated threadable arrangements. In more detail, the clamping-together of the discs, which are mounted on a common cylindrical support member, has been effected by a screw-threaded member for forcing a displaceable member against the battery of discs, supported at its other end by a fixed abutment surface. This method proved unsatisfactory in view of the following considerations: Since a typical disc pack is comprised of, say, 300-400 discs, no absolute assurance of an exact, uniform surface pressure between any pair of discs throughout the pack can be attained. Certain initial dislocations or deformations are necessarily present, and their combined or accumulated effect frequently results in a locally developed gap anywhere along the outer circumferential surface of the filter element. Dirt tending to accumulate within such gap, will in due course gradually infiltrate, pushing for itself more and more room and getting deeper in a wedge-like fashion until a local burst or rupture of the filter occurs. When this happens, the filtering capability of the device as a whole is drastically affected.
Secondly, since the discs are made of plastics, namely of a somewhat elastic material, under the initial tightening force, plastic deformations of each and every disc will after a while take place. Now again, such plastic deformations, tiny as they might be, are multiplied by the number of discs, and the combined loosening effect of the pack as a whole will become noticeable, particularly if the kind of dynamic operation character of the filter is to be taken into account.
One simple and immediate solution to the problem at hand, that would appear effective to eliminate the above-listed disadvantages of the screw-threading tightening method, is to provide the disc pack with spring means urging same in the compacting direction so that it will automatically compensate for every dislocation of the above-mentioned type. However, such solution is impractical because it will call for too strong a spring to achieve the desired effect (in the order of 200-300 Kg.).
It is thus an object of the invention to significantly simplify the construction of and the control over filtering systems comprised of conventional filter elements. It is a further object of the invention to provide a filtering system wherein each filter device thereof will comprise at least two filter elements connected in parallel so that flushing of one of the elements will not affect the operation of the complete filter device, namely, put it out of circulation with respect to the system.
It is a still further object of the invention that flushing cycles will be effected by clean, filtered water.
It is a still further object of the invention that such filter devices be provided with self-controlled filter elements of the discs type, wherein during flushing stages thereof, the discs are separated or released from their compact engagement to be more thoroughly rinsed by reverse flow flushing water.
It is a still further object of the present invention to use hydraulic means that will successfully replace the mechanical means.